An O-ring, also known as a packing, or a toric joint, is a mechanical gasket in the shape of a torus; it is a loop of elastomer with a round cross-section, designed to be seated in a groove and compressed during assembly between two or more parts, creating a seal at the interface. The O-ring may be used in static applications or in dynamic applications where there is relative motion between the parts and the O-ring. Dynamic examples include rotating pump shafts and hydraulic cylinder pistons. O-rings are one of the most common seals used in machine design because they are inexpensive, easy to make, and reliable and have simple mounting requirements. They can seal tens of megapascals (thousands of psi) of pressure.

An oak is a tree or shrub in the genus Quercus (; Latin "oak tree") of the beech family, Fagaceae. There are approximately 600 extant species of oaks. The common name "oak" also appears in the names of species in related genera, notably Lithocarpus (stone oaks), as well as in those of unrelated species such as Grevillea robusta (silky oaks) and the Casuarinaceae (she-oaks). The genus Quercus is native to the Northern Hemisphere, and includes deciduous and evergreen species extending from cool temperate to tropical latitudes in the Americas, Asia, Europe, and North Africa. North America contains the largest number of oak species, with approximately 90 occurring in the United States, while Mexico has 160 species of which 109 are endemic. The second greatest center of oak diversity is China, which contains approximately 100 species. Oaks have spirally arranged leaves, with lobate margins in many species; some have serrated leaves or entire leaf with smooth margins. Also, the acorns contain tannic acid, as do the leaves, which helps to guard from fungi and insects. Many deciduous species are marcescent, not dropping dead leaves until spring. In spring, a single oak tree produces both male flowers (in the form of catkins) and small female flowers. The fruit is a nut called an acorn or oak nut borne in a cup-like structure known as a cupule; each acorn contains one seed (rarely two or three) and takes 6–18 months to mature, depending on their species. The live oaks are distinguished for being evergreen, but are not actually a distinct group and instead are dispersed across the genus.

OASIS International is an American company that manufactures drinking water coolers, non-refrigerated water fountains, bottled water dispensers, and dehumidifiers in North America, Asia, and the EMEA regions. Its head office is in Columbus, Ohio and it has production facilities in Monterrey and Gliwice. It also has its European headquarters in Ballina and a permanent office in Shenzhen. The company's history dates to 1910, when it was founded as the "D.A. Ebinger Sanitary Manufacturing Company," and later known as "EBCO." It renamed itself "Oasis" after its popular product lines in 1996.

Oboes ( OH-boh) belong to the classification of double reed woodwind instruments. Oboes are usually made of wood, but there are also oboes made of synthetic materials. The most common oboe plays in the treble or soprano range. A soprano oboe measures roughly 65 cm (25 1⁄2 in) long, with metal keys, a conical bore and a flared bell. Sound is produced by blowing into the reed at a sufficient air pressure, causing it to vibrate with the air column. The distinctive tone is versatile and has been described as "bright". When the word oboe is used alone, it is generally taken to mean the treble instrument rather than other instruments of the family, such as the bass oboe, the cor anglais (English horn), or oboe d'amore A musician who plays the oboe is called an oboist. Today, the oboe is commonly used in concert bands, orchestras, chamber music, film music, some genres of folk music, and as a solo instrument, and occasionally heard in jazz, rock, pop, and popular music.

An ocean (from Ancient Greek Ὠκεανός, transc. Okeanós) is a body of water that composes much of a planet's hydrosphere. On Earth, an ocean is one of the major conventional divisions of the World Ocean. These are, in descending order by area, the Pacific, Atlantic, Indian, Southern (Antarctic), and Arctic Oceans. The word "ocean" is often used interchangeably with "sea" in American English. Strictly speaking, a sea is a body of water (generally a division of the world ocean) partly or fully enclosed by land, though "the sea" refers also to the oceans. Saline water covers approximately 361,000,000 km2 (139,000,000 sq mi) and is customarily divided into several principal oceans and smaller seas, with the ocean covering approximately 71% of Earth's surface and 90% of the Earth's biosphere. The ocean contains 97% of Earth's water, and oceanographers have stated that less than 5% of the World Ocean has been explored. The total volume is approximately 1.35 billion cubic kilometers (320 million cu mi) with an average depth of nearly 3,700 meters (12,100 ft).As the world ocean is the principal component of Earth's hydrosphere, it is integral to life, forms part of the carbon cycle, and influences climate and weather patterns. The World Ocean is the habitat of 230,000 known species, but because much of it is unexplored, the number of species that exist in the ocean is much larger, possibly over two million. The origin of Earth's oceans is unknown; oceans are thought to have formed in the Hadean eon and may have been the impetus for the emergence of life. Extraterrestrial oceans may be composed of water or other elements and compounds. The only confirmed large stable bodies of extraterrestrial surface liquids are the lakes of Titan, although there is evidence for the existence of oceans elsewhere in the Solar System. Early in their geologic histories, Mars and Venus are theorized to have had large water oceans. The Mars ocean hypothesis suggests that nearly a third of the surface of Mars was once covered by water, and a runaway greenhouse effect may have boiled away the global ocean of Venus. Compounds such as salts and ammonia dissolved in water lower its freezing point so that water might exist in large quantities in extraterrestrial environments as brine or convecting ice. Unconfirmed oceans are speculated beneath the surface of many dwarf planets and natural satellites; notably, the ocean of Europa is estimated to have over twice the water volume of Earth. The Solar System's giant planets are also thought to have liquid atmospheric layers of yet to be confirmed compositions. Oceans may also exist on exoplanets and exomoons, including surface oceans of liquid water within a circumstellar habitable zone. Ocean planets are a hypothetical type of planet with a surface completely covered with liquid.

Oceania (UK: , US: (listen), ) is a geographic region which includes Australasia, Melanesia, Micronesia and Polynesia. Spanning the eastern and western hemispheres, Oceania covers an area of 8,525,989 square kilometres (3,291,903 sq mi) and has a population of 40 million. Situated in the southeast of the Asia-Pacific region, Oceania, when compared to continental regions, is the smallest in land area and the second smallest in population after Antarctica. Definitions of Oceania vary; however, the islands at the geographic extremes of Oceania are generally considered to be the Bonin Islands, a politically integral part of Japan; Hawaii, a state of the United States; Clipperton Island, a possession of France; the Juan Fernández Islands, belonging to Chile; and Macquarie Island, belonging to Australia. (The United Nations has its own geopolitical definition of Oceania, but this consists of discrete political entities, and so excludes the Bonin Islands, Hawaii, Clipperton Island, and the Juan Fernández Islands, along with Easter Island.) Oceania has a diverse mix of economies from the highly developed and globally competitive financial markets of Australia and New Zealand, which rank high in quality of life and human development index, to the much less developed economies that belong to countries such as Kiribati and Tuvalu, while also including medium-sized economies of Pacific islands such as Palau, Fiji and Tonga. The largest and most populous country in Oceania is Australia, with Sydney being the largest city of both Oceania and Australia.The first settlers of Australia, New Guinea, and the large islands just to the east arrived more than 60,000 years ago. Oceania was first explored by Europeans from the 16th century onward. Portuguese navigators, between 1512 and 1526, reached the Tanimbar Islands, some of the Caroline Islands and west Papua New Guinea. On his first voyage in the 18th century, James Cook, who later arrived at the highly developed Hawaiian Islands, went to Tahiti and followed the east coast of Australia for the first time. The Pacific front saw major action during the Second World War, mainly between Allied powers the United States and Australia, and Axis power Japan. The arrival of European settlers in subsequent centuries resulted in a significant alteration in the social and political landscape of Oceania. In more contemporary times there has been increasing discussion on national flags and a desire by some Oceanians to display their distinguishable and individualistic identity. The rock art of Australian Aborigines is the longest continuously practiced artistic tradition in the world. Puncak Jaya in Papua is often considered the highest peak in Oceania. Most Oceanian countries have a parliamentary representative democratic multi-party system, with tourism being a large source of income for the Pacific Islands nations.

The Oceanium is a public aquarium that opened in 2001 in Diergaarde Blijdorp, a zoo in Rotterdam, Netherlands. The Oceanium lies in the expansion area of the zoo, which includes a new entrance and parking area, and was the biggest project to date for the zoo. The area around the Oceanium is home to projects depicting the Americas. The Oceanium is also home to scientific research into the conservation of coral.

Oceanvolt is a Finnish boat electric motor manufacturer founded in 2004 by Janne Kjellman. The company was formerly known as Electric Ocean. Oceanvolt is headquartered in Vantaa, Finland. The company currently produces two types of propulsion systems for electric boats: saildrives and shaftdrives. Oceanvolt has received several awards for its SD8.6 saildrive system, the latest being the 2013 Pittman Innovation Award given by SAIL Magazine for Oceanvolt's "compact robust design" featuring waterproof permanent magnet motor with closed circulation liquid cooling, single lever control with motor status shown by LEDs, and folding propeller which doubles as a hydrogenerator, silently extracting several kilowatts of electric power from the boat's forward motion while under sail.

The octopus ( or ~) is a soft-bodied, eight-armed mollusc of the order Octopoda. Around 300 species are recognised and the order is grouped within the class Cephalopoda with squids, cuttlefish and nautiloids. Like other cephalopods, the octopus is bilaterally symmetric with two eyes and a beak, with its mouth at the centre point of the arms (which are sometimes mistakenly called "tentacles"). The soft body can rapidly alter its shape, enabling octopuses to squeeze through small gaps. They trail their eight arms behind them as they swim. The siphon is used both for respiration and for locomotion, by expelling a jet of water. Octopuses have a complex nervous system and excellent sight, and are among the most intelligent and behaviourally diverse of all invertebrates. Octopuses inhabit various regions of the ocean, including coral reefs, pelagic waters, and the seabed; some live in the intertidal zone and others at abyssal depths. Most species grow fast, mature early and are short-lived. During breeding, the male uses a specially adapted arm to deliver a bundle of sperm directly into the female's mantle cavity, after which he becomes senescent and dies. The female deposits fertilised eggs in a den and cares for them until they hatch, after which she also dies. Strategies to defend themselves against predators include the expulsion of ink, the use of camouflage and threat displays, their ability to jet quickly through the water, and their ability to hide. All octopuses are venomous, but only the blue-ringed octopuses are known to be deadly to humans. Octopuses appear in mythology as sea monsters like the Kraken of Norway and the Akkorokamui of the Ainu, and probably the Gorgon of ancient Greece. A battle with an octopus appears in Victor Hugo's book Toilers of the Sea, inspiring other works such as Ian Fleming's Octopussy. Octopuses appear in Japanese erotic art, shunga. They are eaten by humans in many parts of the world, especially the Mediterranean and the Asian seas.

Odoo is an all-in-one management software that offers a range of business applications that form a complete suite of enterprise management applications. The Odoo solution is ideal for SMEs, but fits both small and large companies alike. Odoo is an all-in-one business software capable of covering all business needs, including CRM, Website/e-Commerce, billing, accounting, manufacturing, warehouse- and project management, and inventory, all seamlessly integrated. Odoo offers three separate versions of the solution; Odoo Enterprise, Odoo Online SaaS (Software as a Service) version, and the Odoo Community version. The Enterprise version is self hosted, it includes all the apps, and the pricing starts at $360 per user per year, with a minimum of 5 users. The Odoo Online version is hosted on a cloud, and the first app is offered for free as a standalone app for unlimited users. After the first app, there is a fixed monthly subscription fee for the apps used and the number of users. The Community version is the open source version. The Source code for the OpenObject framework and core ERP (enterprise resource planning) modules is curated by the Belgium-based Odoo S.A. The last fully featured Open Source version was 8.0 (LTS), available on GitHub under AGPLv3. Odoo is the most popular open source ERP system.